media: uapi: pisp_be_config: Add extra config fields

Complete the pisp_be_config strcture by adding fields that even if not
written to the HW are relevant to complete the uAPI and put it in par
with the BSP driver.

Fixes: c6c49bac ("media: uapi: Add Raspberry Pi PiSP Back End uAPI")
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>